A PHPDoc type for the $payment argument of the  \Paymill\Models\Response\Client::setPayment() method is wrong

```
@param \Paymill\Models\Response\Payment $payment
```

https://github.com/paymill/paymill-php/blob/v4.4.1/lib/Paymill/Models/Response/Client.php#L90

It is wrong, because the method can accept an array (a [list of payments](https://developers.paymill.com/API/index#-client-object)) as a  $payment argument value.

Related to https://github.com/paymill/paymill-php/issues/139